IDCS J1426.5+3508: SUNYAEV–ZEL’DOVICH MEASUREMENT OF A MASSIVE INFRARED-SELECTED CLUSTER AT z = 1.75

We report 31 GHz CARMA observations of IDCS J1426.5+3508, an infrared-selected galaxy cluster at z = 1.75. A Sunyaev–Zel'dovich (SZ) decrement is detected toward this cluster, indicating a total mass of M 200, m = (4.3 ± 1.1) × 1014 M☉ in agreement with the approximate X-ray mass of ∼5 × 1014 M☉. IDCS J1426.5+3508 is by far the most distant cluster yet detected via the SZ effect, and the most massive z ⩾ 1.4 galaxy cluster found to date. Despite the mere ∼1% probability of finding it in the 8.82 deg2 IRAC Distant Cluster Survey, IDCS J1426.5+3508 is not completely unexpected in ΛCDM once the area of large, existing surveys is considered. IDCS J1426.5+3508 is, however, among the rarest, most extreme clusters ever discovered and indeed is an evolutionary precursor to the most massive known clusters at all redshifts. We discuss how imminent, highly sensitive SZ experiments will complement infrared techniques for statistical studies of the formation of the most massive galaxy clusters in the z > 1.5 universe, including potential precursors to IDCS J1426.5+3508.